It is common to periodically measure the load on the rod string of a well unit so that an analysis of the well characteristics and of the performance of the pumping unit can be made. This is normally done by mounting two different transducers to the pumping unit, one of which supplies a signal which is proportional to the vertical position of the pumping unit and the other of which supplies a signal which is proportional to the load on the rod string. The position transducer commonly is mounted on the polish rod of the rod string at a location below the carrier bar, while the quantitative load transducer is mounted on the polish rod between the polish rod clamp and the carrier bar.
The installation of the quantitative load transducer is difficult in situations where there is little space available on the polish rod to receive the transducer or to maneuver the rod in order to expose more of the rod. This problem is frequently encountered where there is a high wellhead completion, leaving little room between the wellhead and the pumping unit, and where the basic design of the pumping unit similarly leaves little room.
One solution to the problem has been to physically raise the entire pumping unit and install additional concrete bases beneath it to permanently maintain it in the raised position. This provides more exposed polish rod space but is an expensive method which is preferably to be avoided. Another solution has been to use a pulling unit t raise the rod and remove rod blow-out preventers. This is not only time consuming and expensive but is also potentially hazardous in that the removal of the rod blow-out preventers allows gas from the well to escape. Another solution has been to raise the polish rod clamp, while still secured to the polish rod, a sufficient distance to allow the transducer to be inserted on the polish rod at a location above the carrier bar. After running the dynamometer survey the transducer has been removed and the clamp moved to its original position.
Although the latter method is normally preferred over the other methods mentioned, it also has definite drawbacks. It is time consuming to move the polish rod clamp as required, which allows the well to recover. Thereafter, the well must be monitored until it has stabilized, with the result that the time required for this entire procedure can be a great deal longer than the time it would normally take to run the dynamometer. Moreover, it cannot be employed in the situation wherein there is insufficient room between the carrier bar, the liner nut and the stuffing box to enable the polish rod clamp to be lifted the necessary distance to enable the transducer to be inserted. In addition, even in cases where the clamp can be lifted a sufficient amount, by doing so the pump attached to the rod string is lifted a like distance, with the result that the test is run with the pump plunger in a higher than normal position in the pump barrel, which can have an effect on the dynamometer results.
It would be desirable to be able to quickly and conveniently install a dynamometer transducer on the polish rod of a well unit which does not have sufficient room between the carrier bar and the elements on the rod beneath it to normally allow this to be accomplished.